Aquarium Soil

You need to be careful about aquarium soil. Some of leaches ammonia for round 6 months, so you can't have fish in the tank until it stops. Other's alter the water chemistry. And most of them become ineffective after about a year, having used up any nutrients in them, so you then have to start using root tabs.

Unless someone else can suggest an aquarium soil that doesn't leach ammonia or change the water conditions, I wouldn't bother with one.

I used Westland Aquatic Compost in my 300 litre pond. It contains a mixture of loam and fine grit and nutrients. It does contain some lime based ingredients so it will alter water chemistry. My tap water is very hard and it didn’t affect the pH when I added it to the pond in baskets.  Didn’t notice any change in the background Ammonia readings from my Seneye when I first introduced it.
I was considering using it in a nano tank setup covered with fine gravel to prevent it from clouding the water.
It did cloud the water in the pond for about a day after adding the baskets.

What you are after is a product with a high Cation Exchange Capacity or CEC. This refers to the ability of the soil to absorb and release nutrients. An aquatic soil which contains nutrients may be useful for starting a tank but it is certainly not essential. As long as you have a soil with a high CEC rating (you can find these with a bit of googling) then the soil will absorb nutrients from the water column and fish poo etc and make it readily available to the plant roots.

Your choice depends on the type of plants you want to grow. If the plants are stem or floating plants for example then these plants take their nutrients mainly from the waters column and so having nutrients at the base is less important. If you wish to use rosette and bulb planta auxh as crypts and swords though (which are easy to care for plants generally) then nutrients at the base are more important because these are heavy root feeders. 

You can definately use root tabs under heavy root feeding plants though as these provide useful nutrients at locations specific to the plants which require it and simply need replacing normally every 3 to 6 months once exhausted. They are most useful with deep rooting plants, carpeting plants which cover a large area with shallow roots will be less suitable to this form of substrate.

As you are talking about scaping a tank without removing the fish at this stage doing a nutrient rich base layer and capping this with another substrate will not be feasible. This also applies to products which leach ammonia which could kill your livestock.

Updated to add:
Some soils are designed to reduce pH because this aids absorption of carbon dioxide into the water. I personally don't believe this is something to worry about too much, provided you do not cause a significant and quick pH swing which your livestock would not appreciate.

Manufacturers normally recommend how many bags you need for a size of aquarium though you can also calculate this yourself using the volume calculators on this site if you replace the height of your tank with the depth of substrate you require.

Thanks for all the replies guys. All very useful information I have asked a couple of shops about Cation Exchange Capacity and neither of heard of it. But will do the google research and look at the other soils mentioned by everyone.

There is a possibility I might transfer fish from one of my tank into the other, there is only 3, and very similar tank to help with replacement substrate.

Most shops are OK on general things like filters, heaters and plain ordinary gravel but not specialised things like aquascaping stuff. You are better getting that on-line, and asking for advice from aquascaping experts like Matt.

Shops are also useless on fish 

I am going to aquascape  my nano tank for shrimp and have invested in Dennerle Nutribasis 6in1 topped with Dennerle quartz black gravel.

The sand area in my set up is sand top to bottom Helen, so I can't chip in with an answer to that...  Gravel on soil certainly remains in place though... 

I'm fairly sure my kuhlis are the culprits, but where the move the sand on top of the gravel, it sinks, so I can't move it back.

Hi barneyadi,

I use Tetra Complete Substrate topped with JBL Manado, both of which have performed well in my setup. Check out the full specification of each of these products in order to be sure they are what you are looking for. I also recommend you take a look at https://www.ukaps.org/index.php?page=guide-to-substrates.

JPC